It is common for off-road vehicles to drive through a body of water and this is often referred to as a wading event. Driver caution and judgement is required when navigating a vehicle through a body of water at wading depth, i.e. at a depth at which the vehicle can be considered to be wading. This is because a vehicle driver does not generally know the depth of water the vehicle is about to enter or the nature of the terrain below the water surface. This is particularly so in low visibility conditions (dirty water, low-light, heavy rain, fog). It is recommended that a survey of the terrain is taken by wading through water on foot, but factors such as the variability of the terrain; low visibility conditions; inconvenience to the driver; and driver impatience may result in a driver attempting to traverse water without knowledge of the water depth and therefore without being able to take appropriate precautions.
In development of vehicle systems intended to aid a drivers control of a vehicle when wading through water, the present applicant has submitted a series of patent applications relating to the detection of a body of water using one or more sensors mounted externally on the vehicle. For example, in WO 2012/123555 a vehicle having a system comprising two ultrasonic transducer sensors, disposed on the left-side and right-side mirrors of the vehicle, operable in conjunction with an under-body mounted contact water sensor, is disclosed.
The present applicant has also submitted patent applications relating to the use of an in-vehicle cabin display screen for providing information to the driver of the vehicle. For example, in WO/2012/080435, WO/2012/080437 and WO/2012/080438 each to the present applicant, vehicles having display systems are disclosed in which an elevation of a vehicle is shown along with a current water level and data relating to a maximum wading depth and an advisory vehicle speed respectively.
It can be appreciated that the more data that is gathered regarding the detection of water and measurements relating to its depth relative to the vehicle, the more accurate a system for aiding wading may be. However, such data needs to be processed and analysed in real-time and in such a way that the data output on a display screen provides useful information in a clear and easily understood manner. It has been disclosed in WO/2012/080435. WO/2012/080437 and WO/2012/080438 to illustrate a detected water level by showing a straight line on an elevation of a display vehicle. Whilst a straight line representing a water level is a simple graphic which is easy for the driver to review and assimilate the necessary information, the determination of where to place such a line is not straightforward. This is especially so given the fact that the actual water being detected does not adopt a perfectly flat, smooth surface and is especially so when data from multiple sources regarding water level is obtained at different points across a moving, rippled and non-flat water surface.
The present invention in at least some embodiments seeks to provide a further improvement in systems for land-based vehicles for aiding driver control of those vehicles when wading.